1. Field of the Invention
The present invention relates to a method for forming thin metal films, and more specifically, it relates to a method for forming thin metal films for wiring.
2. Description of the Related Art
For forming high integration and high speed LSIs, the design of the LSIs becomes more exacting, so that as the width of wires and the diameter of via holes decrease, there results an increase of the aspect ration. As a method of embedding the grooves for wires and the via holes, there has been developed a method for forming metal films by chemical vapor deposition technique which in principle provides excellent step coverage.
An example of conventional formation methods of thin metal films is shown in FIG. 2. This conventional example is described in "Proceedings of VLSI Multilevel Interconnection Conference", 1993, p. 463-469. According to this formation method of thin metal films, an insulating film 102 is first deposited all over the surface of a substrate 101 as shown in FIG. 2(a), and a via hole 104 is then bored. In succession, a barrier metal 103 is deposited. Next, an aluminum film 105 is deposited in accordance with a chemical vapor deposition technique using dimethylaluminum-hydride. At this time, a void 106 occasionally is formed in the via hole 104, as shown in FIG. 2(b). The formation of the void is caused by the fact that the aluminum film deposited by the chemical vapor deposition technique has a rough surface. That is to say, in the course of the deposition of the aluminum film, the surface of the aluminum film is chapped, and recesses of the film come in contact with each other in the upper portion of the via hole, whereby the feed of raw material to the inside of the via hole is blocked, so that the recesses remain in the form of the void.
In the above-mentioned conventional example, current density increases due to the void in the via hole, so that the migration phenomenon of an aluminum atom by current called electromigration increases, with the result that wires are liable to be broken and the reliability of the wiring deteriorates inconveniently.